The present invention relates to bicycle shifters and more particularly to a bicycle shifter having tooth segments for takeup, retention and release of a shifting cable that are arranged on one disk element.
Trigger shifters are typically used to pull and release a spring-loaded shifting cable, and biased to return to their original positions after they are actuated. Trigger shifters are disclosed in patents EP 0 361 335 B1 and U.S. Pat. No. 6,095,010. The shifters disclosed in these patents have two levers, a takeup lever to wind the spring-loaded shifting cable and a release lever to disengage positioning and retaining devices to release or unwind the shifting cable. The takeup lever rotates a takeup or cable spool by actuating a pawl biased in an engagement direction. The takeup spool is preloaded in the unwinding direction by a return spring acting on the shifting cable. The positioning device retains the takeup spool in a particular shift position, thereby counteracting the return force on the shifting cable.
The positioning device of EP 0 361 335 B1 includes a disk element that is connected nonrotatably to a cable spool and has two tooth segments. First and second pawls alternately engage the two tooth segments, respectively. The release operation is accomplished in two stages: the first pawl, initially engaged, is disengaged from the first tooth segment allowing the disk to rotate with the cable spool until the second pawl engages the second tooth segment. When the release lever returns to its initial position, the second pawl is disengaged from the second tooth segment allowing the disk element to further unwind until the first pawl once again engages the first tooth segment.
The positioning device disclosed in U.S. Pat. No. 6,095,010 includes first and second disk elements that are connected nonrotatably to the cable spool and are engageable by first and second latching lugs, respectively, of the release lever. Upon actuation of the release lever, the positioning device is disengaged to permit unwinding or release of the shift cable. The release operation takes place in two stages: the first latching lug, initially engaged, is disengaged from the tooth segment of the first disk element as the second latching lug engages the tooth segment of the second disk element. The first and second disk elements rotate with the cable spool until the second latching lug engages the corresponding retaining tooth of the second disk element. When the release lever returns to its starting position, the second latching lug is disengaged from the tooth segment of the second disk element and the cable spool continues to rotate until the first latching lug engages a next retaining tooth of the first disk element. After actuation, both levers are returned to their original positions by a return spring. During the takeup operation, the spring-loaded pawl ratchets over the sawtooth contours of the tooth segment on the second disk element.
The above shifters require three peripheral tooth segments to implement the shifting operation. One tooth segment is used for the takeup operation, the other two tooth segments for the retention and release operations. Several problems are associated with these types of shifters. For example, only two tooth segments may be arranged on the periphery of a disk element because of the multiple gear ratios, thereby requiring a second disk element for the third tooth segment.
Another problem is that many components are needed for the takeup and release operations. For example, the shifter must have a takeup lever with a return spring, a cable spool operably connected to multiple disk elements, a positioning device with locking pawls and a preloaded spring, and a release lever with a return spring. Such a large number of components need to be precisely coordinated with each other, are costly to manufacture and assemble, and require a larger shifter housing.